The phenomena whereby an electro-optical material such as a liquid crystal is caused to vary its transmissivity in response to an applied electrical potential is adaptable for use in visual displays of information such as television, computer graphics, variable light transmitting shutters, etc. While display devices embodying these principles are well known, problems associated with the manufacture of such devices have limited their practicality. One such problem is the high frequency with which short circuits appear across the fluid layer, particularly when made thin to achieve lower voltage operation. Such short circuits are usually a result of an inability to control the contact spacing through the fluid layer.
Additionally, it has been found that some liquid crystals deteriorate rapidly unless hermetically sealed within the display from the environment. The requirement of a hermetic seal adds complexity in the fabrication process of prior art devices by limiting the constituent elements to inorganic compounds.
A further problem is the difficulty in providing consistency in the transmissive qualities of the liquid crystal under varying contact voltages. Since the light transmitting properties of the liquid crystal fluid depend upon the voltage gradient within the fluid, and in turn the contact spacing, to provide a consistency in transmissivity, it is important to accurately control the spacing between contacts through the fluid for uniformity. This is particularly true where the light transmitting properties depend non-linearly on the voltage gradient, and saturation is not desired. Also, an unevenness in spacing concentrates the effect of the applied voltage in regions of closest contact spacing and promotes a more rapid deterioration in the fluid in addition to the uneven optical properties.
Because of these and other problems, the manufacture of reliable, long life liquid crystal display structures has been very difficult. Particularly difficult, and yet very desirable, is the provision of a thin consistent fluid layer. This, as noted, provides in combination the advantages of increased light scattering effects at lower voltages, more uniform contrast between light transparent and light scattering segments of a display, and avoidance of uneven current densities which decrease device life.
Finally, control of the spacing between the electrical contacts is critical where one contact is a non-plane surface and the other contact is made flexible to allow it to conform to the non-plane surface. In this case, accurate spacing cannot be achieved by conventional methods.